The present invention relates to a process for recovery of gallium using a chelate resin from aqueous solution containing gallium. More particularly, it relates to an economical process for recovery of highly pure gallium from aqueous solution containing the same using a chelate resin.
In general, gallium is industrially produced from aqueous sodium aluminate solution, so-called Bayer's solution available from the process of alumina production. This is a very useful raw material because gallium concentration in the Bayer's solution is about 10-500 mg/l.
Hitherto, there are two principal processes for recovery of gallium from this Bayer's solution, namely, (1) electrolyzing the Bayer's solution using mercury as a cathode to convert gallium in the solution to an amalgam, hydrolyzing this amalgam with caustic alkali and then electrolyzing the resulting aqueous alkali gallate solution and (2) precipitating mainly alumina component in the Bayer's solution to increase the proportions of gallium component to alumina component, blowing carbon dioxide into this solution to coprecipitate alumina component and gallium component, dissolving this coprecipitate in caustic alkali and then electrolyzing the resulting aqueous alkali gallate solution. In addition to the above, a process for recovery of gallium from the Bayer's solution has been proposed in which liquid-liquid extraction is effected between aqueous sodium aluminate solution with an extraction solvent comprising an organic solvent and an extractant consisting essentially of a water-insoluble substituted hydroxyquinoline. [cf. Japanese Patent Unexamined Publication (Kokai) Nos. 32411/76, 52289/78 and 99726/79].
The inventors have proposed a process for recovery of gallium using a chelate resin having an amidoxime group [Japanese Patent Unexamined Publication (Kokai) No. 49620/83], a process using a chelate resin having (A) an =NOH group and (B) a functional group capable of forming a chelate bond with said functional group (A) through gallium [Japanese Patent Unexamined Publication (Kokai) No. 52450/83]and a process using a chelate resin having oxine ligand [Japanese Patent Unexamined Publication (Kokai) No. 96831/83].
Furthermore, a process for increase of selective adsorptivity for gallium in aqueous solution containing impurity metals is passing the aqueous solution containing gallium through a chelate resin at an SV (superficial velocity in a column) of 5 hr.sup.-1 or less. [Japanese Patent Unexamined Publication (Kokai) No. 42737/83].
However, the process of electrolysis with mercury as an cathode as above has the problem that a large amount of mercury dissolves in aqueous sodium aluminate solution and thus is lost during amalgamation. The process of coprecipitation by blowing carbon dioxide also has the problem that the use of carbon dioxide causes carbonization of caustic alkali component in the aqueous sodium aluminate solution, resulting in loss of the caustic alkali. Therefore, these processes are industrially not necessarily satisfactory.
The process of liquid-liquid extraction above has the defects that recovery of gallium per reactants used is industrially not sufficient or selective adsorptivity for gallium is not necessarily high. Furthermore, since the chemical used for recovery of gallium is liquid, a considerable amount of the chemical is dissolved in aqueous sodium aluminate solution and is lost.
The processes for recovery of gallium by various chelate resins which have been proposed by the inventors are superior in selectivity to gallium in aqueous solution containing other impurity metals, but further improvement of adsorptivity has been expected.
The process of passing the solution at SV=5 hr.sup.-1 or less as above has also the problems that the process is hardly applied when chelate resins employed are inferior in chemical resistance and heat resistance and besides it is not economical because of reduction in producibility per unit time, since increase of selective adsorptivity is attempted by reducing the flowing rate.